This invention relates to shock absorbers and more particularly to piston-cylinder shock absorbers defining therewithin a variable volume fluid confining chamber, in which the axial load on the shock absorber may be ascertained by measuring the fluid pressure in such chamber.
This invention is an improvement over my previous U.S. Pat. No. 3,652,040, which issued Mar. 28, 1972, for a "LANDING GEAR SHOCK STRUT". The present invention, like the invention set forth in the above-identified U.S. Pat., is intended for minimizing frictional effects between the piston and cylinder of an aircraft shock strut, also referred to as an oleo strut, to afford an accurate measurement of the weight load carried by the strut. Typically, the shock strut includes a cylinder member and a piston member telescopically reciprocable therein, and defining therebetween a variable volume, fluid confining chamber adapted to receive one or more fluids, including compressible gasses such as air and incompressible liquids such as oil. The resulting structure affords various shock absorbing effects, such as spring cushioning and damping, desirable during landing and ground handling of the aircraft.
When the aircraft is at rest, the loaded weight thereof bears substantially axially on the shock strut, creating a counteracting fluid pressure force in the above-mentioned strut chamber. As is known, this internal fluid pressure can be measured to ascertain the magnitude of the weight or load resting on each of the shock struts, and from these measurements, the weight and balance of the aircraft can be computed.
It is also known, however, that the measurement of the fluid pressure is not always an accurate indication of the weight carried by the shock strut inasmuch as axially oriented frictional forces developed between the piston and cylinder introduce errors in the correlation between the fluid pressure and the load. In my aforementioned U.S. Pat. No. 3,652,040, these piston-cylinder frictional forces were substantially reduced by producing an oscillatory, relative rotation between the cylinder and piston members by a hydraulic actuator acting on the pivotal, apex joint of the torque linkage interconnecting the cylinder and piston members.
However, when the oscillatory actuator force is applied at the apex joint of the torque restraint linkage, a specially designed apex joint is required which must bear the rather substantial torque restraining loads that occur between the aircraft wheel or wheels, carried at the lower end of the strut piston, and the strut cylinder mounted to the aircraft body.
Additionally, the actuator in my U.S. Pat. No. 3,652,040 operates by effecting a relative rotation between the piston and cylinder. However, the main landing gears of many aircraft are not rotatably mounted with respect to the supporting shock strut cylinder. In such case, the only way to achieve the necessary relative rotation, is to cause a certain amount of pivotal tire deflection as the actuator rotates the piston relative to the strut cylinder. The resilience of the tire or tires does permit limited rotation of the shock strut piston relative to the stationary cylinder and aircraft body. However, for relatively large aircraft, and particularly those having multiple wheels on each landing gear, an undesirably large actuator force is required to achieve sufficient rotational displacement, especially when the wheel brakes are locked.